At first, we create a new combo widget object. You already could
pass the array of data in the constructor if you wanted to, but
here we use the set_array() method to do this.
After providing the data, entry with id 2 is made
active/pre-selected.

Whenever the selection changes, the example displays the selected
key and value in a label below the combo box. We use
get_active_key() to retrieve the key, and
get_active_text() to retrieve the value.